title: N-methylpurine DNA glycosylase and DNA polymerase beta modulate BER inhibitor potentiation of glioma cells to temozolomide.
abstract: Temozolomide (TMZ) is the preferred chemotherapeutic agent in the treatment of glioma following surgical resection and/or radiation. Resistance to TMZ is attributed to efficient repair and/or tolerance of TMZ-induced DNA lesions. The majority of the TMZ-induced DNA base adducts are repaired by the base excision repair (BER) pathway and therefore modulation of this pathway can enhance drug sensitivity. N-methylpurine DNA glycosylase (MPG) initiates BER by removing TMZ-induced N3-methyladenine and N7-methylguanine base lesions, leaving abasic sites (AP sites) in DNA for further processing by BER. Using the human glioma cell lines LN428 and T98G, we report here that potentiation of TMZ via BER inhibition [methoxyamine (MX), the PARP inhibitors PJ34 and ABT-888 or depletion (knockdown) of PARG] is greatly enhanced by over-expression of the BER initiating enzyme MPG. We also show that methoxyamine-induced potentiation of TMZ in MPG expressing glioma cells is abrogated by elevated-expression of the rate-limiting BER enzyme DNA polymerase β (Polβ), suggesting that cells proficient for BER readily repair AP sites in the presence of MX. Further, depletion of Polβ increases PARP inhibitor-induced potentiation in the MPG over-expressing glioma cells, suggesting that expression of Polβ modulates the cytotoxic effect of combining increased repair initiation and BER inhibition. This study demonstrates that MPG overexpression, together with inhibition of BER, sensitizes glioma cells to the alkylating agent TMZ in a Polβ-dependent manner, suggesting that the expression level of both MPG and Polβ might be used to predict the effectiveness of MX and PARP-mediated potentiation of TMZ in cancer treatment.
authors.affiliation: Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
authors.forename: Jiang-bo
authors.initials: JB
authors.lastname: Tang
authors.forename: David
authors.initials: D
authors.lastname: Svilar
authors.forename: Ram N
authors.initials: RN
authors.lastname: Trivedi
authors.forename: Xiao-hong
authors.initials: XH
authors.lastname: Wang
authors.forename: Eva M
authors.initials: EM
authors.lastname: Goellner
authors.forename: Briana
authors.initials: B
authors.lastname: Moore
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Hamilton
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Banze
authors.forename: Ashley R
authors.initials: AR
authors.lastname: Brown
authors.forename: Robert W
authors.initials: RW
authors.lastname: Sobol
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001921:Brain / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D001932:Brain Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D045647:DNA Glycosylases / Q000235:genetics / Q000378:metabolism*; D015254:DNA Modification Methylases / Q000235:genetics; D019951:DNA Polymerase beta / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000187:drug effects*; D045643:DNA Repair Enzymes / Q000235:genetics; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004357:Drug Synergism; D005910:Glioma / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D006147:Guanine / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D006898:Hydroxylamines / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077204:Temozolomide; D025521:Tumor Suppressor Proteins / Q000235:genetics
chemical_list: D018906:Antineoplastic Agents, Alkylating; D006898:Hydroxylamines; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins; D006147:Guanine; C008450:7-methylguanine; D003606:Dacarbazine; C005214:methoxyamine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D019951:DNA Polymerase beta; D045647:DNA Glycosylases; D045643:DNA Repair Enzymes; D000077204:Temozolomide